My favorite book in the entire world is 'A Wizard's dozen' by a collaboration of authors. I love the fact that it's a book of awesome short stories. It has everything magical in it, from fairies to wizards, and dragons to sea nymphs. This book was my fantasy world.
Another amazing book that had me trapped in it for years is 'Others See Us' by William Sleator. It may look really cheesy from the front, but I swear it's a GREAT BOOK!
Super book number three belongs to 'House of Stairs'. Another book by William Sleator, but great as well!
Teriffic book number four is saved for the entire Harry Potter collection! These books are amazing!
And Last, but not least, 'Secret of Spring' by Piers Anthony. Awesome book! I loved every page!